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Spatial and Temporal Control of Hyperthermia Using Real Time Ultrasonic Thermal Strain Imaging with Motion Compensation, Phantom Study.

Foiret J, Ferrara KW - PLoS ONE (2015)

Bottom Line: However, combined ultrasound imaging and therapy systems offer the benefits of simple, low-cost devices that can be broadly applied.Here, we propose a motion compensation method based on the acquisition of multiple reference frames prior to treatment.The technique was tested in the presence of 2-D and 3-D physiological-scale motion and was found to provide effective real-time temperature monitoring.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, University of California Davis, Davis, CA, United States of America.

ABSTRACT
Mild hyperthermia has been successfully employed to induce reversible physiological changes that can directly treat cancer and enhance local drug delivery. In this approach, temperature monitoring is essential to avoid undesirable biological effects that result from thermal damage. For thermal therapies, Magnetic Resonance Imaging (MRI) has been employed to control real-time Focused Ultrasound (FUS) therapies. However, combined ultrasound imaging and therapy systems offer the benefits of simple, low-cost devices that can be broadly applied. To facilitate such technology, ultrasound thermometry has potential to reliably monitor temperature. Control of mild hyperthermia was previously achieved using a proportional-integral-derivative (PID) controller based on thermocouple measurements. Despite accurate temporal control of heating, this method is limited by the single position at which the temperature is measured. Ultrasound thermometry techniques based on exploiting the thermal dependence of acoustic parameters (such as longitudinal velocity) can be extended to create thermal maps and allow an accurate monitoring of temperature with good spatial resolution. However, in vivo applications of this technique have not been fully developed due to the high sensitivity to tissue motion. Here, we propose a motion compensation method based on the acquisition of multiple reference frames prior to treatment. The technique was tested in the presence of 2-D and 3-D physiological-scale motion and was found to provide effective real-time temperature monitoring. PID control of mild hyperthermia in presence of motion was then tested with ultrasound thermometry as feedback and temperature was maintained within 0.3°C of the requested value.

No MeSH data available.


Related in: MedlinePlus

Processing steps between the apparent displacement map and the final temperature map.First the raw apparent displacement map was calculated (A), and then the equation of a plane was fit outside of the heated area to estimate the compression of the tissue (B). The resulting map was then subtracted from the raw apparent displacement map (C). The corrected map was then smoothed (D) and the axial gradient was calculated to get the thermal strain map (E). Using the calibration value, the temperature map is superimposed on the B-mode image (F). This example presents the correction applied for a periodical linear axial compression inducing a 7.5% mechanical strain on the phantom.
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pone.0134938.g003: Processing steps between the apparent displacement map and the final temperature map.First the raw apparent displacement map was calculated (A), and then the equation of a plane was fit outside of the heated area to estimate the compression of the tissue (B). The resulting map was then subtracted from the raw apparent displacement map (C). The corrected map was then smoothed (D) and the axial gradient was calculated to get the thermal strain map (E). Using the calibration value, the temperature map is superimposed on the B-mode image (F). This example presents the correction applied for a periodical linear axial compression inducing a 7.5% mechanical strain on the phantom.

Mentions: An estimate of the axial lag induced by tissue motion was calculated and subtracted from the shift map leaving only the apparent displacement induced by the change in temperature. During this step, a plane was fitted to the axial displacement map by estimating the coefficients a, b and c of the equation:Δdmotion(x,z)=ax+bz+c(5)and then subtracted from the displacement map as depicted in Fig 3. During this process, the heated area was not included in the calculation. This process particularly helps to differentiate tissue motion from apparent displacement in the case of axial compression. The map was then successively smoothed with a 1-D Savitzky-Golay filter [41] in the lateral and axial dimensions with window sizes of respectively 11λ and 17λ (3.4 and 5.2 mm). The thermal strain map was finally obtained by differentiating the apparent displacement map in the axial dimension.


Spatial and Temporal Control of Hyperthermia Using Real Time Ultrasonic Thermal Strain Imaging with Motion Compensation, Phantom Study.

Foiret J, Ferrara KW - PLoS ONE (2015)

Processing steps between the apparent displacement map and the final temperature map.First the raw apparent displacement map was calculated (A), and then the equation of a plane was fit outside of the heated area to estimate the compression of the tissue (B). The resulting map was then subtracted from the raw apparent displacement map (C). The corrected map was then smoothed (D) and the axial gradient was calculated to get the thermal strain map (E). Using the calibration value, the temperature map is superimposed on the B-mode image (F). This example presents the correction applied for a periodical linear axial compression inducing a 7.5% mechanical strain on the phantom.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4526517&req=5

pone.0134938.g003: Processing steps between the apparent displacement map and the final temperature map.First the raw apparent displacement map was calculated (A), and then the equation of a plane was fit outside of the heated area to estimate the compression of the tissue (B). The resulting map was then subtracted from the raw apparent displacement map (C). The corrected map was then smoothed (D) and the axial gradient was calculated to get the thermal strain map (E). Using the calibration value, the temperature map is superimposed on the B-mode image (F). This example presents the correction applied for a periodical linear axial compression inducing a 7.5% mechanical strain on the phantom.
Mentions: An estimate of the axial lag induced by tissue motion was calculated and subtracted from the shift map leaving only the apparent displacement induced by the change in temperature. During this step, a plane was fitted to the axial displacement map by estimating the coefficients a, b and c of the equation:Δdmotion(x,z)=ax+bz+c(5)and then subtracted from the displacement map as depicted in Fig 3. During this process, the heated area was not included in the calculation. This process particularly helps to differentiate tissue motion from apparent displacement in the case of axial compression. The map was then successively smoothed with a 1-D Savitzky-Golay filter [41] in the lateral and axial dimensions with window sizes of respectively 11λ and 17λ (3.4 and 5.2 mm). The thermal strain map was finally obtained by differentiating the apparent displacement map in the axial dimension.

Bottom Line: However, combined ultrasound imaging and therapy systems offer the benefits of simple, low-cost devices that can be broadly applied.Here, we propose a motion compensation method based on the acquisition of multiple reference frames prior to treatment.The technique was tested in the presence of 2-D and 3-D physiological-scale motion and was found to provide effective real-time temperature monitoring.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, University of California Davis, Davis, CA, United States of America.

ABSTRACT
Mild hyperthermia has been successfully employed to induce reversible physiological changes that can directly treat cancer and enhance local drug delivery. In this approach, temperature monitoring is essential to avoid undesirable biological effects that result from thermal damage. For thermal therapies, Magnetic Resonance Imaging (MRI) has been employed to control real-time Focused Ultrasound (FUS) therapies. However, combined ultrasound imaging and therapy systems offer the benefits of simple, low-cost devices that can be broadly applied. To facilitate such technology, ultrasound thermometry has potential to reliably monitor temperature. Control of mild hyperthermia was previously achieved using a proportional-integral-derivative (PID) controller based on thermocouple measurements. Despite accurate temporal control of heating, this method is limited by the single position at which the temperature is measured. Ultrasound thermometry techniques based on exploiting the thermal dependence of acoustic parameters (such as longitudinal velocity) can be extended to create thermal maps and allow an accurate monitoring of temperature with good spatial resolution. However, in vivo applications of this technique have not been fully developed due to the high sensitivity to tissue motion. Here, we propose a motion compensation method based on the acquisition of multiple reference frames prior to treatment. The technique was tested in the presence of 2-D and 3-D physiological-scale motion and was found to provide effective real-time temperature monitoring. PID control of mild hyperthermia in presence of motion was then tested with ultrasound thermometry as feedback and temperature was maintained within 0.3°C of the requested value.

No MeSH data available.


Related in: MedlinePlus